Two-cycle engine sleeve valve control of scavenging



Sept. 26, 1950 E. E. K. s'PARMANN TWO-CYCLE ENGINE SLEEVE VALVE CONTROL 0F' SCAVENGING Filed Nov. l2s, 194s `2 Sheets`-Sheet 1 Sept. 26, 1950 v E. E. K. sPARMANN 2,523,599

'Two-CYCLE ENGINE sLEEvE vALvE coNTEoL 0E scAvENGING Filed Nov. 26. 1946 2 Shee'ts--Sheet 2 Patented Sept. 26, 1950 Two CYCLE ENGINE SLEEVE VALVE .CONTROL oF soAvENGING Edmund Ernst Karl Sparmann,I Stockholm, Sweden Application November 26, 194s, serial No. tisss In Sweden November 27, 1945 oiaims. (c1, V12s- 65) The present invention relates to two-cycle motors and particularly to anovel control ofthe inlet and exhaust ports of such motors, and has .as its main object to avoid to a great extent certain disadvantages which so far have been inherent in two-cycle engines. l

According to the present invention, the 4twocycle motor comprises, in combination, a working cylinder provided with .exhaust ports nea-r its outer end which are controlled by -openings of a sleeve valve surrounding the piston and periodically passing said ports, andwith inlet or scavenging `ports near its inner end which are controlled by the combined movement of the upper edge of the piston and of openings provided in the sleeve valve and periodically :passing said ports, meansbeing provided to impart to each point of the sleeve valve an oscillatory Ymovement at least partially deviating from the .direction `of the axis of the cylinder, said oscillatory movement being considerably accelerated in axial .direction during the scavenging period,`but having va small acceleration in axial direction during the compression and combustion periods, when the inlet and exhaust ports in the cylinder .are closed, the movement of the sleeve valve being slightly .inadvance of the movement of the piston.

There have already been proposed `twocycle engines with sleeve valve control which are pro.- vided with certain of the above features in combination with other arrangements, resulting however in direct disadvantages or dangerous conditions of operation, or which exclude the possibility of obtaining motors with high .power ratings. The combination of all the features ac.- cording tothe present invention'results ina considerable improvement of the scavenging .process and in a more reliable operation, even for highly rated two-cycle motors, that is to say, with .motors running at high speed and operating at Yhigh effective pressures, or 'highly supercharged.

The accompanying drawings show by Yway of example and diagrammatically some of the numerous vpractical embodiments ofthe present -invention, and the lmanner of applicationof the invention to different types of motors, such as motors with the cylinders arranged in lineradia:lV

cylinder motors or wobbler engines having the working 4cylinders disposed axially around' the engine shaft.

Figs. 1, 2, 3 and 4 each show an axial section through the working cylinder of a two-.cycle 4engine ,according to the invention atdiienent'positions of operationof the piston; the arrangement shown can be used for one-cylinder engines orfoi` engines having the cylinders disposed in line..

, Fig. 5 shows the lower portion of a working cylinder according to a modication which may be used for one-cylinder engines or for radial cylinder motors. This example further discloses means for improving the `scavenging process or for supercharging the cylinder.

, Figs. 6 and 7 show transverse sections through the working cylinder along the lines V I-'VI, and

f VII- VIL respectively, of Fig. V5.

Fig. 8 represents a modication of the invention for use with wobbler engines.

InFigs l and 4 the working cylinder l is shown in `axial section; its cylinder head penetrates like a plug into the vupper portion of the cylinder, while a narrow `annular space 3 is provided `between the head and the cylinder wall. The ,upper end `of asleeve valve 4 disposed between the piston 5 and the cylinder wall, is slidably engaged the space 3 lso `as to :be 1gas tight. The piston 5 reciprocates within the sleeve valve 4 and is connected by the connecting rod E and the crank to the motor shaft l.

In Figs. l to 4 a smaller crank drive is represented in 4proximity to the base of the cylinder, ,this crank drive having a crank shaft ,9 Which will be called control shaft hereinafter, and a crank pin l0. The control shaft l0 is driven in @EY conventional manner, not illustrated, by the motor shaft l, and with the same number of revolutions as the motor shaft, but not necessarilyin the same direction. In Figs. 1 to 4 the control shaftv lo and the motor shaft 1 are assumed to turn in ,opposite directions, as indicated by the arrows on the figures.

The crank pin l0 is connected to a small ,connecting rod `Il which impar-ts an oscillating ,moe .tion to an arm I3 pivoted on a .pi-n .l 4. The pin i4 is mounted on any suitable stationary part of the motor. lI'he connecting rod Il is articulated by means of a ,pin ,l2 on the oscillating arm I.3. The oscillating arm I3 is connected b y means of an universal ioint l5 to a radially projecting cylindrical bolt I6 .of the sleeve valve-.4, the universel joint .i5 being at the same time axially slidable on the bolt lli.` Naturally, the bolt could also be arranged on the oscillating arm and would. then b e axially slidable in ,an universal joint mounted on the sleeve valve.

As vseen from Figs. 1 to .4, particularly from Fig. 2, the crank pin l0 is angularly displaced throughapproximately relative to the .crank pin 8 of the motor shalt, so that whenthe .crank 'pin `il of the motor shaft 'lV is in proximity of the lower (inner) dead center, then the crank pin I of the control shaft is near its outer dead center.

This phase displacement of the two crank drives has the effect that the axial acceleration of the sleeve valve 4 reaches a maximum, while the motor piston 5, in proximity to its lower dead center, has a relatively small acceleration, and vice versa. By a suitable selection of the different angles and of the ratios in the crank and link mechanism for the sleeve valve motion, this inverse relation of acceleration between the sleeve valve and the piston can still be considerably increased. Such an arrangement makes it possible, even with a relatively small stroke of the sleeve valve, to obtain relatively great flow sections of the inlet and exhaust ports. This result, in combination with the principle of unidirectional flow of scavenging here used, permits an effective scavenging and a good charge of the working cylinder. Naturally, the sleeve Valve will have a small advance relative to the piston. The sleeve will pass its lower (inner) dead center about to 40 ahead of the working piston.

The control of the exhaust and inlet ports is effected in the following manner: A series of exhaust ports I8 is provided in the upper portion of the cylinder I, and a series of inlet or scavenging ports I9 is provided at the lower end of the working space in the cylinder. The ports |9 can be in communication with the crank case,

if the latter is used for scavenging, or they can be connected to a separate scavenging pump or to a compressor. Also the sleeve valve 4 is provided with two series of openings and 2| the axial distance between the two series corresponding substantially to that between the exhaust and inlet ports in the cylinder and will be varied according to the control diagram desired by the engine designer. The openings 20 in the sleeve 4 cooperate with the exhaust ports I8, and the openings 2I with the inlet ports I9.

In Fig. 1 the motor cylinder is diagrammatically drawn in a position in which the exhaust ports 20 of the sleeve valve 4 just emerge from their protected and cooled position in the annular space 3 between the cylinder wall and the cylinder head, in which they move during the compression and expansion periods. When the motor shaft 'I turns in the direction of the arrow, the exhaust ports now open always further. Though the piston 5 is already slightly below the upper edge of the scavenging and inlet ports I9 at the bottom of the cylinder, the inlet openings 2| of the sleeve valve 4 are still closed by the piston. Owing to the greater crank radius and to the greater angular distance of the crank pin 8 from its lower dead center, the piston 5 now moves relatively faster than the sleeve valve 4.

In Fig. 2 the piston 5 has caught up with the movement of the sleeve valve 4 to the extent that upper edge of the piston is at the same level as the upper edge of the inlet openings 2| of the sleeve valve. The movement of the sleeve is now extremely slight, because its crank drive, as chosen in the represented example, is only about 5 before its dead center position, but the crank pin 8 of the motor shaft is still about 20 before its lower dead center position. Meanwhile the exhaust ports I8 in the upper part of the cylinder have been continuously uncovered by the outlet openings 20 of the sleeve 4, and the major portion-of the exhaust gases can have left the cylinder space before fresh air or combustible mixture can enter the cylinder at the lower end of the working space and expel the remainder of the burnt gases through the still considerably opened exhaust ports at the top of the cylinder, the scavenging system operating according to the principle of unidirectional flow having proved to be the most effective system.

In Fig. 3 the sleeve 4, owing to its advance and to its greater relative acceleration, has travelled so far that the outlet openings 20, of the sleeve 4 start to enter the annular space 3 between cylinder wall and cylinder head, and accordingly the exhaust openings in the cylinder are completely closed again, while the phase displacement between piston and sleeve movement, and the characteristics of the sleeve motion, function to first fully open the inlet ports I9 and then to gradually close them, since the upper edge of the piston head reaches the upper edge of inlet openings 2|.

This position is represented in Fig. 4, in which the working space of the cylinder is also closed at the bottom and compression starts. The exhaust openings 20 in the sleeve valve have in the meanwhile moved upwardly so far that the sleeve 4 ensures a tight closure at the top of the cylinder, while during the entire compression and combustion periods the end of the sleeve provided with the outlet openings moves between the cooled surfaces of the cylinder head and the cylinder wall, so that the portion of the sleeve which is exposed to extreme heating during the exhaust period will be effectively cooled for a relatively long period.

In the example represented in Figs. 1 to 4 it is not a question of obtaining an optimum for the high efficiency of the scavenging diagram, illustrated on the crank circle of Fig. 4. The exhaust opens at about 70 before lower dead center, the inlet or scavenging opens only 40 later, thus about 30 before lower dead center of the piston movement; afterwards during about the exhaust and the inlet are both open, the exhaust ports closing about 25 after lower dead center, and only later, at about 85 after lower dead center the inlet ports also close. The relatively long period of pre-exhaust, the considerable period of admission or supercharging, if desired, the scavenging according to unidirectional flow, in combination with the relatively large open now sections, permit an eicient scavenging and emptying of the cylinder of combustion gases and considerable lowering of the gas pressure before the admission of fresh air or fresh combustion mixture, and the scavenging and admission is effected without any change in direction of flow along the shortest path. The relatively long admission period provides a high degree of lling of the working space before the beginning of the compression period, or when using a compressor, an effective supercharging, enabling high outputs to be obtained or maintenance of the capacity at high altitudes.

A further feature of the invention consists in the fact that the movement of the sleeve valve is not only characterised by a particular acceleration at a predetermined point of its stroke, but that the sleeve effects an oscillatory movement along a path which deviates from the axial direction. It is advantageous to shape the path of this oscillatory movement of the sleeve in such manner that during the scavenging period this path deviates less from the axial direction than during the compression and combustion periods. By this provision a number of substantial advantages are realised as compared with similar known sleeve valve control systems,

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while at` the saine time the deficiencies of these known control systems are avoided. A movementof the sleeve valve which is parallel' to the axis, has the disadvantage of favoring the formation of scores or burrsyon the sleeve or on the piston, and catching of the piston rings on the edges ofthe ports. The circular sleeve movement (for example according to Burt McCollum, Ricardo or others) has the disadvantage that the effective maximum flow' section of the ports is considerably smaller than the sectional; areas of the openings provided in the sleeve and in the cylinder. The effective sectional areas of fl'ow not only remain smaller, but result` in,l a throttling of the gas flow and disturb this ow by creatingy a turbulence, even when the ports and openings are situated relative to each other in the position for maximum opening. Moreover the transverse movement, that is, the tangential component of the sleeve movement, is undesirably great from the standpoint of thev construction and operation of theslieeve drive. On the other hand, the circular movement of'the sleeve has the great advantage 0i"v a good redistribution of the lubricating oil film` and results accordingly in an improved lubricatiom and in a more4 uniform distribution of" temperature over the circumference ofthe sleeve valve, as wellas the piston and the cylinder, While scoring of the sleeve and piston,

and catching of the piston rings is avoided.-

The combination of the particular conditions ofiacceleration of the sleeve movement with a certain predetermined path of this movement, according to the invention, not only incorporates atfthe same time the advantages ofthe different known systems and avoids their disadvantages, butin addition to this, the movement of the sleeve. valve during the scavenging4 period',4 that is., While the ports are open, deviates little from the axial direction, and when the ports areclosed deviates relatively more from this direction, so that the axial component of the sleeye movement is relatively greater when the ports are open and it is, desired to attain quickly openings of" large section, while the axial component of the sleeve motion is further reduced by the greater deviation fromjthe axial direction when the ports are closed' andan axialmovement of the sleevevalve is not desired, be-

cause this movement only increases thel lengthV paths of the sleeve motion is not limitedv to anyy determined constructions and' can be otherwise than illustrated. In Figs. 1` to lel the sleeve movement is obtained by the particularcontrol' shaft'V Sfr and the oscillatory arm I3pivoted on the pin I'4'; s o that the connecting point I5 on the sleeve 4` oscill'ates along a circular arc andall points;

of' the sleeve valve accordingly describe circular arc-shaped paths.

Also in the example according to Fig. 5, all` points ofI the sleeve valve -4 oscillate along circular paths. In this example; however,` no specialV control shaft isprovided' formovingthef sleeve,

which is drivenV bya cra-nkA or eccentric, I or;

the motorL Shaft 1f; having a smaller-radiusthan the crank 8- for` the pistonandl being correyti'onsof acceleration of the sleeve valve 4, theL :sol

d' spondfngly ldisplaced in phase relative to this crank. In order to obtainV the particular condimotion transmission between the crank I0 andl the sleeve valve comprises a pivoting lever I1 mounted' on a journal pin 22 and connected to the crank Hl by a connectingrod- II, and to the oscillatory arm I3- by a link `24 articulated at 23 to the lever I'I' and at 25 to the arm I3. An

. universal joint I5 'onthe end ofthe arm I3 is `working; cylinder I andl of the sleeve valve 4.

The reversal of the conditions ofiacceleration of the sleeve movement is obtained in this example in principle by means of the pivoting lever I1, andI byM corresponding selection of the angle between the connectingrod I I and the lever IT, as well as between the lever Il, thelink' 2'4v and the oscillatory arm- I3, forming toggle joints, the conditions of acceleration orV the dead center positions of the sleeveV can still be further modied', that is to say, a comparatively greater acceleration of the, oscillatoryV sleeve movement can beV obtained at the lower dead center than at the upperdead center. The arrangement illustrated. is particularly'suitable for radial cylinder engines,y or for one-cylinder engines when the use of a special control shaft isto be avoided.

Fig. 5 also shows how the designer, if he. de,- sires,4 can'` make use ofthe unsymmetric control diagram to proceed rst vvith` scavenging by pure air in carburetted motors, Vand charge or supery charge only afterwardsy withr combustible. mixture, when by timely closure of the exhaustports there is no possi-bilityV of` a loss of fresh gases. Theannular inlet conduit at the bottom ofthe cylinder can then be divided, by a partition 26 in twosuperposed separate conduits I9 and I9". In order to obtain a thorough mixture, the wall sections between the inlet ports canbe formed as guide blades which, for increasingv the turbulence of the incoming gas stream, can be oppositely inclined relative to the center of. the cylinderV in thetwo superposed series of ports,y or at least the directions of ow of two superposed ports will', deviate one with respect to theV athen. as shown in Figs. 6 and '7.

Besides thearrangements shown-in Figs. 1 to 4 and 5 forobtaining the characteristic motion and" acceleration conditions for the sleeve valve according to the, invention, many other modifications and combinations may be used, by the provision-*of* guide levers, slot and crank drives, toggle, j ointsor other guide link motions.

A further modification is shown by way ofexample in Fig. Swhich moreover discloses the ap,- plicati'on of the invention ton Wobbler engines having; cylinders I disposed aroundA the motor shaft or the, crank; shaft infthe previous examples'.

The; motor cylinder I is not shown in section.

as; it is situated in the rear of the plane ofV the gurej whenV point` Ill" and the motor shaftY T" are assumed* to besituated in the plane of'the'draw' ing, and the rotation of the Shaft 1 is assumed to be in clockwise direction when viewed from the drawing) has not been represented as itr forms no part of the invention. Also, only one of the cylinders has been shown.

.The motor` shaft 'F is mounted in thevengine casing 28 partially shown in section. The crank pin of the wobbler drive, as is well known, is inclined relative to the motor shaft, whereby the wobbler plate body executes its characteristic wobbling motion about its center, on which it is mounted on the ball joint 29. The wobbler plate body must be prevented by any suitable means from rotating relative to the engine casing, so that the connecting pins 8 for the pistons describe an oscillating movement in axial direction according to a spacial lemniscate., Other points of the wobbler plate body not situated in the wobbler plate plane describe slightly deviating unsymmetrical spacial loop curves, as for example the point Ill the movement of which is represented by the dash and dot line |69, the

line |80' representing this movement in another projection, as seen from the left in Fig. 8.

Owing to the spacial curved path of the connecting point I from which the sleeve valve motion is derived, the connecting rod II must be provided with universal joints at both of its ends, at the point of connection I to the wobbler plate body, and at the point I2 where the connecting rod is articulated to a link 3U rotatably mounted on the engine casing. It would be possible for realising the movement of the sleeve according to the invention to couple the point I2 directly with the sleeve and-to obtain the sleeve motion by the guide link 3|). The paths of all points of the sleeve would then again be circular arcs as in the previous examples, or other lines, according to the kind of guide link which is used.

The guide link motion as represented in Fig. 8 isv particularly suitable for obtaining a favorable sleeve motion. The free ends of the two links 3U and 32 -mounted on the engine casing, are

shaft 'I rotates and the point I 0 of the wobbler plate describes its path Ill0, the universal joint I5, through the medium of the illustrated link motion which is some kind of lemniscoidal motion, describes a so-called coupling curve, illustrated in Fig. 8 by the dash and dot line I 50. This curve I'E is approximately a straight line in its lower portion, but deviates quite suddenly from the straight direction in its upper portion. Each point of the sleeve valve describes a corresponding path which fully corresponds to the object to be attained by the invention. The desired conditions of acceleration are already substantially obtained inpart by a suitable selection of the transmission ratios and the angles between the members of the guide motion 30, I3, 7

32, but these conditions are still further accentuated by the shape of the paths of ail points of the sleevev (accordingly also of its ports 20 and 2i) as determined by the guide motion; accordingly during the scavenging period the sleeve valve' effects a relative intensive acceleration in axial direction, while during the compression and the combustion periods a reduced axial movement, but a moderate rotation of the sleeve valve is realised, which angular movement is useful for distributing the oil lm and im-proving the temperature compensation, as well as for preventing the formation of scores on the piston. on the sleeve valve and on the cylinder wall.

Thel phase displacement for the required advance of the sleeve motion relative to the motor shaft is obtained by placing the connecting point Ill for coupling the wobbler plate to the sleeve in a meridian plane which, according to the desired advance of the sleeve, is situated angularly in advance of the connecting point B of the corresponding -piston, so that the point IIJ upon rotation of the motor shaft 'I arrives at its lower or inner dead center ahead of the corresponding piston.

The invention can be applied to motors with special ignition means or to Diesel type engines and is independent of the type of scavenging of the cylinders. The crank case may be used as a scavenging pump, or a separate scavenging pump or compressor may be employed.

The invention almost completely avoids the essential drawbacks which two-cycle motors heretofore always have had, even the greater heat stresses which are inherent in two-stroke cycle engines. The production of heat cannot be avoided, but the detrimental effects thereof can be reduced, as for example the extremely high piston temperatures and the accumulation of heat in proximity of the exhaust ports. Since the piston does not control the exhaust ports, it is not heated by the exhaust gases, which do not pass out of the cylinder in proximity to the piston head; the piston rings are less subject to be locked by burning, and the oifl lm between the piston, the sleeve valve and the cylinder are not burned away; the piston operates in a substantially cooler zone of the cylinder, while the parts of the sleeve valve situated close to the exhaust ports, are exposed to increased heating during the scavenging period only and are cooled during a relatively greater period of time on both external and internal sides by intimate contact with the cooled surfaces of the cylinder wall and cylinder head.

The unusually great sectional areas of the ports (above of the piston area at a ratio of 1:1.25 between diameter and stroke), the considerable relief of exhaust gas pressure before entrance of the inlet ports, the short and straight gas paths owing to unidirectional scavenging, as Well as the possibility of supercharging allow a change of gas and a degree of admission to be obtained which approaches that of four-stroke cycle engines. The conditions of operation for piston, cylinder, sleeve valve and its driving mechanism are extremely favorable. the movements of piston and sleeve valves have mostly the same direction, the relative velocity is smaller than the piston speed, the friction and wear of the piston, the sleeve valve and the cylin.

der are reduced, and the sleeve control mechamsm is relieved. Owing to the small relative motion between the sleeve and the cylinder, and the redistribution of the laterally acting piston thrust on the several times greater Sleeve surface, and since the oil film on the sleeve is not subject to deterioration by combustion gases, the cylinder may be of light metal casting without requiring a liner. This not only means a Owing to the fact thatl saving of weight and of cost, but an improvement of the cooling and amore uniform distribution of temperature over the circumference of the cylinder, also in air-cooled engines.

I claim: Y j K 1. In a two-cycle engine, the combination with a working cylinder and a piston reciprocating therein, said cylinder having exhaust ports at its outer end and inlet ports at its innerend, of a sleeve valve surrounding the piston, said `sleeve valve having outlet openings peniodically registering with said exhaust ports inthe cylinder, and inlet openings cooperating withI the upper edge of the piston and periodically registeringY with said inlet ports in the cylinder.the movement of said sleeve valve being slightly in advance of the movement of the piston, and meansV to impart to each point of the sleeve valve an oscillatory motionl along a path at least partially deviating from the direction of the axis of the cylinder,` the said oscillatory motion having a relatively greater acceleration in `axial direction during the scavenging period, and a relatively` smaller acceleration in .axial direction during the .valve having outlet openings periodicallyregistering with said exhaust ports in the cylinder, and inlet openings cooperating with the upper edge of the piston and periodically registering with said inlet ports in the cylinder, the movement of said sleeve valve being slightly in advance of the movement of the piston, a crank mechanism actuated by the engine shaft at the samenumber of revolution as the engine shaft, and movement transmission members between said crank mechanism and said sleeve valve to impart to each'point of the sleeve valve an oscillatory motion along a path at least partially deviating from the direction of the axis of the cylinder, the said oscillatory motion having a relatively greater acceleration in axial direction during the scavenging period, and a relatively smaller acceleration in axial direction during the compression and combustion periods when the inlet and exhaust ports are closed.

4. A two-cycle engine as claimed in claim 3, wherein said movement transmission members between said crank mechanism and sleeve valve comprise a connecting link coupled to the sleeve valve in such manner that the sleeve valve, in the scavenging period when its openings expose and close again the inlet' and exhaust ports in the cylinder, is in proximity of its outer dead center position-in which owing to the cinematic characteristics of crank mechanisms the acceleration of the sleeve motion is relatively greater than in the inner dead center position.

5. A two-cycle engine as claimed in claim 3, wherein the movement transmission members between the crank mechanism and the sleeve valve comprise toggle joints.

6. A two-cycle engine as claimed in claim 3, in which said crank mechanism compriSeS a crank pin mounted on the engine shaft.

7. A two-cycle engine as claimed in claim .3, wherein the movement of the sleeve valve is in advance .of the piston movement at the inner dead center thereof. V

8. In a two-cycle engine, the combination with a working cylinder and a piston reciprocating therein, said cylinder having exhaust ports at its outer end and inlet ports at its inner end. of a sleeve valve surrounding said piston, said sleeve valve having outlet openings periodically regis,- tering with said exhaust ports inthe cylinder, and inlet openings cooperating with the upper edge of the piston and periodically registering with said inlet ports in the cylinder, the movement of said slide valve being slightly in advance of the movement ofthe piston, a wobbler plate drive connecting the piston to the engine shaft, and means for operatively Vconnecting said wobbler plate to the sleeve valve to impart to each point of the sleeve valve an oscillatory motion along a path at least partially deviating from the direction of the axis of the cylinder, the said oscillatory motion having a relatively greater acceleration in axial direction during the scavenging period, and arelatively smaller acceleration in axial direction during thecompression and combustion periods when the inlet and exhaust ports are closed.

9. A two-cycle engine as claimed in claimy 8, comprising a plurality of cylinders each including a sleeve valve, a movement transmission mechanism controlling the motion of each sleeve valve, and coupling means for operatively lconnecting the movement transmission mechanism of each sleeve valve to a particular point of said wobbler plate.

10. A two-cycle engine as claimed in claim 8, comprising a plurality of cylinders each having a piston reciprocating therein, a connecting rod for operatively coupling each piston to a point 4of the wobbler plate, a sleeve valve .mounted between each piston and Jvcorresponding cylinder, and means for operatively connecting each sleeve valve to a point of said wobbler plate situated angularly in advance of the point of connection of the corresponding piston to the wobbler plate with respect to the direction of movement of the engine shaft.

11. In a two-cycle engine, the combination with a working cylinder and a piston reciprocating therein, said cylinder having exhaust ports at its outer end and inlet ports at its inner end, said inlet ports comprising two series of axially superposed ports, of a sleeve valve surrounding the piston, said sleeve valve having outlet openings periodically registering with said exhaust ports in the cylinder, andinlet openings cooperating with the upper edge of the piston and registering during the scavenging period rst with the inner one of said series of ports and then withthe outer one of said series of ports, the movement of said sleeve valve being slightly ink advance of the movement of the piston, and means to impart to each point of the. sleeve valve an oscillatory motion along a path at least partially deviating from the direction of the axis of the cylinder, the said oscillatory motion having a relatively greater acceleration in axial direction during the scavenging period, and a relatively smaller acceleration in axial direction during the compression and combustion periods when the inlet and exhaust ports are closed.

12. In a two-cycle engine, the combination with a working cylinder and a piston reciprocating therein, said cylinder having exhaust ports at `its outer end and inlet ports at its inner end,

said inlet ports comprising two axially superposed l series of ports with the ports of each series being separated by webs of the cylinder wall extending Ain a different direction from that of the webs of registering during the scavenging period llirst with the inner one of said series of ports and then with the outer one of said series of ports, the movement of said sleeve valve being slightly in advance of the movement of the piston, Yand means to impart to each point of the sleeve valve an oscillatory motion along a path at least partially deviating from the direction of the axis ofl the cylinder, the said oscillatory motion having a relatively greater acceleration in axial direction during the scavenging period,` and a relatively smaller acceleration in axial direction during the compression and vcombustion periods when the inlet and Aexhaust ports are closed.

13. -l'n a two-cycle engine, the combination with a working cylinder and a piston reciprocating therein, said cylinder having exhaust ports at its outer end and inlet ports at its inner end, of a sleeve valvesurrounding the piston, said sleeve valve having outlet openings periodically registering with said exhaust ports in the cylinder, and inlet openings cooperating with the upper edge of the piston and periodically registering with said inlet ports in the cylinder, and motion transmitting mechanism for reciprocating said ,Y

sleeve valve in phase relation with respect to the piston such that the axial movement of the valve ris slightly in advance of that of the piston and hhas greater acceleration in axial direction during the scavenging period of the cycle thanduring the compression and combustion periods of 12 the cycle when the inlet and exhaust ports are closed, said mechanism including means for imparting limited turning movement to the valve during its reciprocatory movements to cause any given point on the valve to travel the same path of movement in both directions of reciprocation.

14. A two-cycle engine as dened in claim 13 wherein the means for imparting said turning movement comprises a member operatively associated with said vsleeve and arranged to oscillate about an anchorage point xed in relation to the cylinder as the sleeve is reciprocated.

15. In a two-cycle piston engine of the kind having inlet and exhaust ports controlled by a sleeve valve, means for reciprocating said valve in predetermined phase relation with respect to the movement of the engine piston, said means comprising motion transmitting mechanism for' REFERENCES CITED The following references are of record in the le of this patent: p

UNITED STATES PATENTS Number Name Date 2,030,213 Kinnucan et al. Feb. 11, 1936 2,072,291 Bischof Mar. 2, 1937 2,134,285 KiiTer Oct. 25, 1938 2,140,454 Howald Dec. 13, 1938 2,230,407 Kammer Feb. 4, 1941 2,236,741 Allyn Apr. 1, 1941 2,242,871 Raab et al May 20, 1941 

